# Calculate Electric Field in Medium

1. Dec 7, 2008

### apalmer3

Hello all! I'm studying for my final, and I'm trying to figure out my teacher's method for the following problem. Could you help me out?

A plane wave is propagating in free space with a frequency of 10 GHz. The amplitude of the electric field in the x-direction is Ex = 2 V m-1.
(ii) Find the magnitude of electric and magnetic field if the plane wave is transmitted through a medium with relative permittivity .

She then goes on to say that you simply need to find the impedance of the material and set H=E/impedance. I realize that this is a true ratio, but shouldn't we have to calculate to magnitude of E in the medium? She uses the value of E in free space, which I think is wrong.

Her answers: E=2 V/m H=11.86 mA/m

2. Dec 10, 2008

### olgranpappy

relative permittivity... what? was there supposed to be a number after the word "permittivity" and before the period?

3. Dec 11, 2008

### Andy Resnick

I really hope there was more to the question than what you typed- as it stands, it's awful.

First, I wonder if the instructor is being cute- the *electric* field in a medium is the same as the electric field in empty space: it is the *displacement* field that is different in matter.

as for the magnetic field, here's how to get there: the magnitude of the magnetic induction B is E/c (c is the speed of light), and the permeability is found from the relationship between the permittivity, permeability, and c:

http://hyperphysics.phy-astr.gsu.edu/Hbase/electric/elefie.html

I didn't run the number to see if that's correct. I bet writing all that down analytically, many extraneous factors cancel which will simplify the calculation.